Method of controlling braking of a vehicle operating in a curved path, and vehicle brake control system

Abstract

To counteract the tendency of over-steering when a vehicle operates in a curved path, and one of the wheels--typically the wheel at the inner side of the curve exhibits a tendency to block and, then, braking pressure is reduced to one of the front wheels only, the braking pressure applied to the rear wheel or wheels is reduced. If braking pessure is reduced to both of the front wheels, braking pressure being applied to the rear wheels is controlled, independently, in accordance with anti-brake lock control considerations, which have priority over dropping of braking pressure to prevent over-steering.

We claim: 
     
       1. In an anti-brake lock system (ABS) for a vehicle, controlling application of braking pressure individually to each of the front wheels and to the rear wheels of the vehicle, a method of controlling braking pressure being applied to the wheels comprising the combination of the steps of;   determining if the vehicle moves in a curved path and deriving a curved path signal;   controlling braking pressure of a first one of the front wheels upon determining in the ABS that said first front wheel has a tendency to block or becomes subject to unstable behavior;   controlling rise in braking pressure at a second front wheel to a predetermined reduced level to thereby decrease yaw torque; and   limiting the braking pressure being applied to the rear wheels as a function of the determination of tendency to block or unstable behavior of said one front wheel if also the curved path signal indicates movement of the vehicle in the curved path.   
     
     
       2. The method of claim 1, wherein said braking pressure limiting step comprises maintaining the braking pressure at the rear wheels essentially constant. 
     
     
       3. The method of claim 2, including the step of lowering the braking pressure being applied to the rear wheels for a predetermined time in advance of maintaining said rear wheels braking pressure constant. 
     
     
       4. The method of claim 2, including the step of lowering the braking pressure being applied to the rear wheels to a predetermined extent in advance of maintaining said braking pressure constant. 
     
     
       5. The method of claim 3, including the step of lowering the braking pressure being applied to the rear wheels to a predetermined extent in advance of maintaining said braking pressure constant. 
     
     
       6. The method of claim 2, including the step of additionally decreasing braking pressure being applied to the rear wheels based on a priority braking pressure decrease commanded by the anti-brake lock system. 
     
     
       7. The method of claim 1, wherein said step of limiting the braking pressure being applied to the rear wheels comprises controlling rise of the braking pressure being applied to the rear wheels to a limited level. 
     
     
       8. The method of claim 7, including the step of lowering the braking pressure being applied to the rear wheels for a predetermined time in advance of said limited level pressure rise. 
     
     
       9. The method of claim 7, including the step of lowering the braking pressure being applied to the rear wheels by a predetermined extent in advance of said limited level pressure. 
     
     
       10. The method of claim 8, including the step of lowering the braking pressure being applied to the rear wheels by a predetermined extent in advance of said limited level pressure rise. 
     
     
       11. The method of claim 7, including the step of controlling the braking pressure level during said limited pressure rise under control of the anti-brake lock system. 
     
     
       12. The method of claim 7, including the step of sensing the level of the curved path signal to determine the extent of transverse acceleration of the vehicle;   and controlling the limited level pressure rise as an inverse function of the extent of transverse acceleration to permit a higher pressure level rise as the transverse acceleration decreases.   
     
     
       13. The method of claim 12, including the step of maintaining the braking pressure at a constant level when a predetermined transverse acceleration is sensed. 
     
     
       14. The method of claim 1, including the step of reducing or suppressing limitation of rise in braking pressure level at the second front wheel if movement of the vehicle in the curved path is determined. 
     
     
       15. The method of claim 14, including the step of reducing or suppressing said limitation of rise in braking pressure level at the second front wheel at relatively high transverse acceleration levels. 
     
     
       16. Anti-brake lock system for a vehicle subject to yaw torque and with reduced tendency to oversteering comprising: means (13) for providing vehicle transverse acceleration signals;   means (1-6), for controlling braking pressure applied to each of the front wheels, independently, and to the rear wheels of the vehicle for preventing locking of any of the wheels;   means (10, 11-15) coupled to and responsive to said braking pressure control means for additionally controlling braking pressure applied to a first one of the front wheels and upon a determination that said first front wheel has a tendency to block or become subject to unstable behavior,   said additional braking pressure control means further controlling rise in braking pressure applied to a second one of the front wheels to a predetermined reduced level upon determining of presence of said transverse acceleration signals, and while braking pressure is applied to said second front wheel under control of said additional braking pressure control means;   rear wheel braking pressure limiting means (9, 20, 21, 23) for limiting the braking pressure being applied to the rear wheels coupled to said braking pressure control means (1-6); and   means (16, 17, 18, 22) coupled to receive said vehicle transverse acceleration signals and further coupled to said rear wheel pressure limiting means for controlling said rear wheel pressure limiting means as a function of the determination of the tendency to block or unstable behavior of said one of said front wheels and while the transverse acceleration signals are present.   
     
     
       17. The system of claim 16, wherein said brake pressure control means for the rear wheels comprises an evaluation circuit (6) sensing operation of the rear wheel or wheels, and controlling, respectively, supply of pressurized brake fluid, maintenance of pressure of the pressurized brake fluid or drainage of pressurized brake fluid from a valve unit means (9) coupled to the rear wheel or wheels;   and wherein signals from said rear wheel evaluation circuit applied to said valve unit means, tending to decrease brake pressure being applied to the rear wheel or wheels, have priority over signals derived from said braking pressure limiting means.